1. Technical Field
This present invention relates to heat pumps, air conditioning and refrigeration equipment. More particularly, the invention relates to diagnostics for identifying indoor fan failure, a dirty indoor filter, a blocked outdoor fan, low refrigerant charge, a stuck expansion valve, and compressor failure.
2. Discussion
The Applicants' assignee has developed a control system for heat pumps that has a decoupled sensor arrangement in which refrigerant is metered through the refrigeration system, based on compressor discharge temperature and ambient air temperature measurements. The sensors are decoupled in that the ambient air temperature and compressor discharge temperature are largely independent of one another. For further information, see U.S. Pat. No. 5,311,748 to Bahel et al., entitled "Control System for Heat Pump Having Decoupled Sensor Arrangement," issued May 17, 1994.
The Applicants' assignee has also developed a control system in which the indoor air flow rate is controlled by a humidity-responsive adjustable speed fan. The control system strives to select the fan speed for optimal operating efficiency and improved occupant comfort. For further details see U.S. Pat. No. 5,303,564 to Bahel et al. entitled "Control System for Heat Pump Having Humidity Responsive Variable Speed Fan," issued Apr. 19, 1994.
The Applicants' assignee has also developed a refrigerant charge detection system or diagnostic system that detects improper amounts of refrigerant (overcharge and undercharge). For further details see U.S. Ser. No. 08/095,897 to Bahel et al. entitled "Overcharge-Undercharge Diagnostic System for Air-Conditioner Controller," filed Jul. 21, 1993.
The Applicants' assignee has also developed a variable capacity compressor system in which compressor discharge temperature, ambient outdoor air temperature and thermal load are used as control parameters for controlling the expansion valve setting and the indoor fan speed. The thermal load parameter can also be used to control the compressor capacity. Thermal load is measured by an integrating procedure that increments or decrements an accumulated demand counter value used as an indication of thermal load on the system. The counter value is incremented and decremented based on the room temperature and thermostat set point. These same parameters are also used in the overcharge/undercharge diagnostic system. For further details see U.S. Ser. No. 08/415,640 to Bahel et al. entitled "Heating and Cooling System With Variable Capacity Compressor", filed Apr. 3, 1995.
Industry demand for improved operation requires more sophisticated diagnostics for identifying faulty system operation to prevent damage to the heat pump system or components thereof and to provide optimum operation and efficiency. Conventional heat pump diagnostic systems operate in a "short-cycling" mode, when certain fault conditions occur, until the user becomes aware of the malfunction. Prolonged short-cycling can adversely affect compressor reliability. Other conventional heat pump diagnostic systems fail to correctly identify fault conditions such as indoor fan failure, a dirty indoor fan filter, a blocked outdoor fan, a stuck-closed expansion valve or low refrigerant charge.